Because of their accuracy and convenience in use, electronic scales with digital readouts are a preferred type of scale, especially in markets where products are sold by weight. Typical scale installations are base-mounted scales atop display cases or in checkout stands, and hanging scales supported from the ceiling.
In base-mounted scales it is possible, but not desirable, to wire them into established electrical circuits to power them. Providing circuits to hanging type scales is considerably more complicated. Hanging electronic scales wired to permanent circuitry are essentially unknown in the marketplace.
The need to wire an electronic scale to permanent circuits can be circumvented by providing battery power instead. However, this seemingly obvious solution is not practical because of the large power demand of these scales as related to the capacity of commercial batteries. Surprisingly, in the course of routine use, a counter scale can readily exhaust a standard radio 9 volt battery in less than a day. This represents a serious operating cost for replacement batteries. Even worse, in stores which have large numbers of scales the inconvenience and distraction of continuously replacing batteries, combined with the labor cost of doing so, have made battery-powered scales, especially hanging scales, unattractive. Many larger stores have literally dozens of hanging scales, and continuously watching them to be certain they are all in working order is simply not practical. It is equally unattractive to have an out-of-service scale in full view, where and when a customer would wish to use it.
As an alternative to permanent power circuits or battery power, there is the photo-voltaic cell. However, prior to this invention they have been impractical for usage in electronic scales. The power generated by a photo-voltaic cell is a function of its area exposed to light, and of the intensity and wavelengths of the light incident upon it. The area that can be made available in a market is severely limited by surrounding structures, the need for clearance space around the scale, and by aesthetics. A very large array projecting widely from a scale, or a large free-standing array, would be absurd in a modern market. If a photo-voltaic array is to be used, it must be small enough to be integrated into the general envelope of the scale.
As a further complication, the light intensity in the modern market is relatively low. While many or most of them have large banks of overhead fluorescent tubes, still the luminous flux at eye-level is surprisingly low, although adequate to its purpose. The power capacity of a photo-voltaic cell must be matched to the requirements of the using circuit in the scale. The small available area and the low light level conspire to render known electronic scales inoperable with photo-voltaic cells, and in turn has frustrated the use of what should be the most attractive power source for a scale.
It is not only relatively small indoor scales which could profit from the use of this power source. Heavier installations, both indoors and outdoors, can profit from it, especially if accumulator means is also provided to store energy for use in periods of lesser or zero light, such as in the evening or at night.
Accordingly, it is an object of this invention to provide eletronic weighing apparatus whose demand for power is within the range of a sensibly-sized photo-voltaic array. Then all the complexities and complications of permanenet circuits and of batteries are avoided. Maintenance of the device is reduced to keeping the array clean, and installation problems to that of merely placing the scale where it is wanted.
It is another object of this invention to provide the many advantages of electronic scales, such as automatic zero compensation, tare entry, and unit of measure selection, in a low power configuration, so low in fact, that it can operate on power derived from relatively small photo-voltaic arrays operated in low intensity light installations.